Inherit Class Dynamicly

Laura Creighton lac at strakt.com
Wed Feb 6 13:15:05 CET 2002


I was really tired when I posted that article yesterday and misunderstood
what you wanted.  Apologies.  I think that this will be more to your liking:

> > Hi, everybody,
> > 
> > from Tkinter import *
> > class NewWidget:
> >         ...
> >         def __init__(self, widget_name = "Button", **dict):
> >                 # What is needed here to make the new born object(self) 
> >                 # behavior like both the class specified by widget_name
> >                 # and NewWidget?
> > 
> > Thanks from
> > 
> > Xiao-Qin
> > 

from __future__ import nested_scopes
import Tkinter

class WrappedWidget:
    def __init__(self, frame, widgetType=Tkinter.Label, **kw):
        self._widget=widgetType(frame, **kw)
        self.bind("<ButtonPress-1>", self.gotPressed)
        
    def __getattr__(self, name):
        if name.startswith("__") and name.endswith("__"):
            raise AttributeError, name
        else:
            return getattr(self._widget, name)

    def gotPressed(self, event):
        print 'I got Pressed!'
        self.configure(bg='red')

###########################  
if __name__ == '__main__':

    root = Tkinter.Tk()
    quit = Tkinter.Button(root, text="QUIT", fg="red", command=root.quit)
    quit.pack(side='left')

    Lab=WrappedWidget(root, fg='green', text='Label (default)')
    Lab.pack(side='left', fill='both', expand = 1)

    mydict={'fg':'yellow', 'text':'Button'}
    But=WrappedWidget(root, Tkinter.Button, **mydict)
    But.pack(side='left', fill='both', expand = 1)
    root.mainloop()
--------------------------------------------

This is the decorator pattern.  Boy is it simple in python.

Note, this relies on the behaviour of classic classes, where you search
all the methods in a class _first_, and then if it is not found, you
use the redefined __getattr__.  In 2.2 in new style classes, the 
__getattr__ is looked up _first_ so this will not work.  I haven't
figured out how to make the decorator pattern in 2.2 not classic
patterns yet.

Sorry to have posted half asleep last night.

Laura Creighton




More information about the Python-list mailing list